Prepared for submission to JINST

22nd International Workshop on Radiation Imaging Detectors27 June 2021 to 1 July 2021

Upgrade of the CMS Resistive Plate Chambers for theHigh Luminosity LHC

A. Samalan,𝑎,1 M. Tytgat,𝑎 G.A. Alves,𝑏 F. Marujo,𝑏 F. Torres Da Silva De Araujo,𝑐 E.M. DaCosta,𝑐 D. De Jesus Damiao,𝑐 H. Nogima,𝑐 A. Santoro,𝑐 S. Fonseca De Souza,𝑐 A.Aleksandrov,𝑑 R. Hadjiiska,𝑑 P. Iaydjiev,𝑑 M. Rodozov,𝑑 M. Shopova,𝑑 G. Soultanov,𝑑 M.Bonchev,𝑒 A. Dimitrov,𝑒 L. Litov,𝑒 B. Pavlov,𝑒 P. Petkov,𝑒 A. Petrov,𝑒 S.J. Qian, 𝑓 C. Bernal,𝑔

A. Cabrera,𝑔 J. Fraga,𝑔 A. Sarkar,𝑔 S. Elsayed,ℎ Y. Assran,ℎℎ,ℎℎℎ M. El Sawy,ℎℎ,ℎℎℎℎ M.A.Mahmoud,𝑖 Y. Mohammed,𝑖 C. Combaret, 𝑗 M. Gouzevitch, 𝑗 G. Grenier, 𝑗 I. Laktineh, 𝑗 L.Mirabito, 𝑗 K. Shchablo, 𝑗 I. Bagaturia,𝑘 D. Lomidze,𝑘 I. Lomidze,𝑘 V. Bhatnagar,𝑙 R. Gupta,𝑙 P.Kumari,𝑙 J. Singh,𝑙 V. Amoozegar,𝑚 B. Boghrati,𝑚,𝑚𝑚 M. Ebraimi,𝑚 R. Ghasemi,𝑚 M.Mohammadi Najafabadi,𝑚 E. Zareian,𝑚 M. Abbrescia,𝑛 R. Aly,𝑛 W. Elmetenawee,𝑛 N. DeFilippis,𝑛 A. Gelmi,𝑛 G. Iaselli,𝑛 S. Leszki,𝑛 F. Loddo,𝑛 I. Margjeka,𝑛 G. Pugliese,𝑛 D. Ramos,𝑛

M. Caponero,𝑛𝑛 L. Benussi,𝑜 S. Bianco,𝑜 S. Colafranceschi,𝑜 A. Russo,𝑜 L. Passamonti,𝑜 D.Piccolo,𝑜 D. Pierluigi,𝑜 G. Saviano,𝑜𝑜 S. Buontempo,𝑝 A. Di Crescenzo,𝑝 F. Fienga,𝑝 G. DeLellis,𝑝 L. Lista,𝑝 S. Meola,𝑝 P. Paolucci,𝑝 A. Braghieri,𝑞 P. Salvini,𝑞 P. Montagna,𝑞𝑞 C.Riccardi,𝑞𝑞 P. Vitulo,𝑞𝑞 B. Francois,𝑟 T.J. Kim,𝑟 J. Park,𝑟 S.Y. Choi,𝑠 B. Hong,𝑠 K.S. Lee,𝑠 J.Goh,𝑡 H. Lee,𝑢 J. Eysermans,𝑣 C. Uribe Estrada,𝑣 I. Pedraza,𝑣 H. Castilla-Valdez,𝑤 A.Sanchez-Hernandez,𝑤 C.A. Mondragon Herrera,𝑤 D.A. Perez Navarro,𝑤 G.A. AyalaSanchez,𝑤 S. Carrillo,𝑥 E. Vazquez,𝑥 N. Zaganidis,𝑥 A. Radi,𝑦 A. Ahmad,𝑧 I. Asghar,𝑧 H.Hoorani,𝑧 S. Muhammad,𝑧 M.A. Shah,𝑧 B. Mandelli,𝑧𝑎 R. Guida,𝑧𝑎 I. Crotty𝑎𝑎 on behalf of theCMS collaboration𝑎Ghent University, Dept. of Physics and Astronomy, Proeftuinstraat 86, B-9000 Ghent, Belgium𝑏Centro Brasileiro Pesquisas Fisicas, R. Dr. Xavier Sigaud, 150 - Urca, Rio de Janeiro - RJ, 22290-180,Brazil

𝑐Dep. de Fisica Nuclear e Altas Energias, Instituto de Fisica, Universidade do Estado do Rio de Janeiro,Rua Sao Francisco Xavier, 524, BR - Rio de Janeiro 20559-900, RJ, Brazil

𝑑Bulgarian Academy of Sciences, Inst. for Nucl. Res. and Nucl. Energy, Tzarigradsko shaussee Boulevard72, BG-1784 Sofia, Bulgaria

𝑒Faculty of Physics, University of Sofia, 5 James Bourchier Boulevard, BG-1164 Sofia, Bulgaria𝑓 School of Physics, Peking University, Beijing 100871, China𝑔Universidad de Los Andes, Apartado Aereo 4976, Carrera 1E, no. 18A 10, CO-Bogota, Colombia

1Corresponding author.

arX

iv:2

109.

1433

1v2

[ph

ysic

s.in

s-de

t] 2

Nov

202

1

ℎEgyptian Network for High Energy Physics, Academy of Scientific Research and Technology, 101 KasrEl-Einy St. Cairo Egypt

ℎℎThe British University in Egypt (BUE), Elsherouk City, Suez Desert Road, Cairo 11837- P.O. Box 43, EgyptℎℎℎSuez University, Elsalam City, Suez - Cairo Road, Suez 43522, Egypt

ℎℎℎℎDepartment of Physics, Faculty of Science, Beni-Suef University, Beni-Suef, Egypt𝑖Center for High Energy Physics, Faculty of Science, Fayoum University, 63514 El-Fayoum, Egypt𝑗Univ Lyon, Univ Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822, F-69622, Villeurbanne,France

𝑘Georgian Technical University, 77 Kostava Str., Tbilisi 0175, Georgia𝑙Department of Physics, Punjab University, Chandigarh 160 014, India𝑚School of Particles and Accelerators, Institute for Research in Fundamental Sciences (IPM), P.O. Box

19395-5531, Tehran, Iran𝑚𝑚School of Engineering, Damghan University, Damghan, 3671641167, Iran

𝑛INFN, Sezione di Bari, Via Orabona 4, IT-70126 Bari, Italy𝑛𝑛ENEA, Frascati, Frascati (RM), I-00044, Italy𝑜INFN, Laboratori Nazionali di Frascati (LNF), Via Enrico Fermi 40, IT-00044 Frascati, Italy

𝑜𝑜Dipartimento di Ingegneria Chimica, Materiali e Ambiente, Sapienza Università di Roma, I-00185𝑝INFN, Sezione di Napoli, Complesso Univ. Monte S. Angelo, Via Cintia, IT-80126 Napoli, Italy𝑞INFN, Sezione di Pavia, Via Bassi 6, IT-Pavia, Italy

𝑞𝑞INFN, Sezione di Pavia and University of Pavia, Via Bassi 6, IT-Pavia, Italy𝑟Hanyang University, 222 Wangsimni-ro, Sageun-dong, Seongdong-gu, Seoul, Republic of Korea𝑠Korea University, Department of Physics, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea𝑡Kyung Hee University, 26 Kyungheedae-ro, Hoegi-dong, Dongdaemun-gu, Seoul, Republic of Korea𝑢Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do 16419, Seoul, Republic ofKorea

𝑣Benemerita Universidad Autonoma de Puebla, Puebla, Mexico𝑤Cinvestav, Av. Instituto Politécnico Nacional No. 2508, Colonia San Pedro Zacatenco, CP 07360, Ciudad

de Mexico D.F., Mexico𝑥Universidad Iberoamericana, Mexico City, Mexico𝑦Sultan Qaboos University, Al Khoudh, Muscat 123, Oman𝑧National Centre for Physics, Quaid-i-Azam University, Islamabad, Pakistan

𝑧𝑎CERN, Espl. des Particules 1, 1211 Meyrin, Switzerland𝑎𝑎Dept. of Physics, Wisconsin University, Madison, WI 53706, United States

E-mail: amrutha.samalan@cern.ch

Abstract: During the upcoming High Luminosity phase of the Large Hadron Collider (HL-LHC),the integrated luminosity of the accelerator will increase to 3000 fb−1. The expected experimentalconditions in that period in terms of background rates, event pileup, and the probable aging ofthe current detectors present a challenge for all the existing experiments at the LHC, including theCompact Muon Solenoid (CMS) experiment. To ensure a highly performing muon system for thisperiod, several upgrades of the Resistive Plate Chamber (RPC) system of the CMS are currentlybeing implemented. These include the replacement of the readout system for the present system,and the installation of two new RPC stations with improved chamber and front-end electronicsdesigns. The current overall status of this CMS RPC upgrade project is presented.

Keywords: Compact Muon Solenoid, Gaseous detectors

Contents

1 Upgrade of CMS sub-detector systems: RPCs 1

2 RPC Link System upgrade 2

3 Extension of the RPC system 3

4 Technical specifications of iRPCs 4

5 New front-end electronics for iRPCs 5

6 iRPC demonstrators 5

7 Summary 7

1 Upgrade of CMS sub-detector systems: RPCs

The Large Hadron Collider (LHC) at European Council for Nuclear Research (CERN) was originallydesigned to operate with an instantaneous luminosity of 1034cm−2s−1 and integrated luminosity onthe order of 300 fb−1. Already in the years 2015–2017, the maximum luminosity exceeded thedesign value by a factor of more than 1.7, which brought the CMS subsystems close to theirrate capability limits [1]. During High Luminosity LHC (HL-LHC) operation, the instantaneousluminosity will be increased to 5×1034cm−2s−1, five times the machine’s original design value,and the ultimate performance of the HL-LHC would enable the collection of 400 to 450 fb−1 ofintegrated luminosity per year. This increase in luminosity at the HL-LHC has many implicationsfor the CMS sub-detector systems. It will increase the average pileup, which will result in worsebackground conditions, higher trigger rates, more difficult event reconstruction, and acceleratedaging of components. To guarantee that the performance of the sub-detectors will be maintainedduring the HL-LHC running, CMS has started implementing different upgrades of the presentsystems, including extensions of systems with new chambers.

The current RPCs at CMS are double-gap chambers operated in avalanche mode with a highelectric field. With an excellent intrinsic time resolution of about 1.5 ns, they are mainly used foraccurate timing and fast triggering. Two main upgrades are foreseen for the present RPC system.While the RPC chambers are capable of operating until the end of Phase-2, the link system, whichconnects the front-end board to the trigger processors, must be exchanged, as is explained in section2. In addition, to extend the RPC coverage in the high pseudorapidity ([) region, an improvedversion of the already existing RPCs, referred to as iRPCs, will be installed in the forward regionon the 3rd and 4th endcap disks. Figure 1 shows the region where these new RPCs will be placed(marked by the red box) [2]. New low noise front-end electronics have been introduced for theiRPC readout. Several prototype chambers have been built to validate the new electronics and to

– 1 –

verify the production technology as well as the detector performance and longevity. The presentstatus of the iRPC project is summarized in this paper.

Figure 1: A quadrant of the CMS experiment. The iRPCs will be installed in the region enclosedby the red box [2].

2 RPC Link System upgrade

In the CMS experiment, the RPC chambers are read out, controlled, and monitored through theLink System, which consists of 1592 electronics boards divided in to two kinds: Link Boards (LBs)and Control Boards (CBs). LBs work either as a Master or Slave LB. The present Link System hasbeen running well for more than 13 years. However, after the third LHC Long Shutdown (LS3), itis expected that aging effects will start to appear [3]. In addition, to deal with the higher data rateresulting from the HL-LHC, an increase in the data transmission band width is required, which isnot possible using the present link system. Furthermore, most of the application specific integratedcircuit (ASIC) chips of the link system will be outmoded by that time, and system maintenance willbecome a challenging issue. As such, the current Link System will be replaced by a new, upgradedsystem.

For the new system, the 28-nm Xilinx Kintex-7 was chosen as the best FPGA option. It offersa large amount of digital resources and supports high speed data transmission together with theability to resist radiation [3]. Hence, an industrial version of the Kintex 7K160T was selected.To improve the time resolution of the muon chamber hits to the order of the RPC intrinsic timeresolution, a 96-channel Time to Digital Converter (TDC) based on a combination of the logicelements and ISERDES primitives, was developed and implemented into the Kintex-7. Each TDCchannel consists of 16 divisions or bins. The time resolution of each bin is one sixteenth of eachbunch crossing, i.e. 1.56 ns. In a comparative study between the emulated and expected channelwidths, the time resolution of each bin was compatible with the expectation based on the firmwareemulation. Moreover, the differential and integral non-linearity errors of the TDC were well below0.006 LSB and 0.01 LSB, respectively. Apart from this, the GTX transceivers of the Kintex-7 wereused as a fundamental element to increase the speed of the data transmission line.

– 2 –

3 Extension of the RPC system

During the upcoming HL-LHC operation, the two endcap regions (high [ region) of the CMSexperiment where the magnetic field is lowest will face high muon and background rates. For effi-cient muon triggering and offline particle identification as well as reconstruction, the measurementof a sufficient number of muon hits per track is required. The present muon system of the CMSexperiment consists of 1056 RPC detectors that cover the region up to |[ | = 1.9. To increase theredundancy and robustness of the muon system, iRPCs (RE3/1 and RE4/1) will be installed in theforward region (on station 3 and station 4), extending the RPC coverage from [ = 1.9 to [ = 2.4.Figure 2 shows a schematic view of the RE3/1 chambers mounted on the endcap disks. These newchambers will complement the already existing Cathode Strip Chambers (CSC) ME3/1 and ME4/1.

Figure 2: Schematic view of the RE3/1chambers mounted on the endcap disks [2].

Figure 3: Simulated comparison between the sin-gle muon trigger efficiencies with and without theRPC information, as a function of |[ | [2].

The major motivations behind upgrading the RPC system with iRPCs are: (i) by complementingthe CSC stations, there will be an enhancement in the local muon measurement by adding track hitsand by increasing the lever arm and (ii) the intrinsic time resolution will be improved (by a factorof ∼2) when the measurements of iRPCs are combined with those of the existing CSC chambers.This will improve the background hit rejection, identification, and reconstruction of slowly movingheavy-stable-charged particles. In addition, unlike RPCs, iRPCs will measure the time differencebetween the signals at both ends of each readout strip, offering a better spatial resolution on theorder of a few cm along the strip direction (non-bending projection). Profiting from this improvedtime and spatial resolutions of the additional iRPC hits and combining them with the CSC data, itwill be possible to resolve the issue of low p𝑇 tracks being misidentified as having high transversemomentum. Moreover, including iRPC hits in the trigger primitive stub-finding algorithm increasesthe triggering efficiency by identifying muon hits that the CSCs cannot detect at some values of |[ |due to the presence of high voltage (HV) spacers inside the chambers. The impact of adding theRPC and iRPC hit information to the single muon trigger is shown in Fig. 3. A clear improvement

– 3 –

in the trigger efficiency of around 15% can be observed between |[ | = 2.1 and 2.2.

4 Technical specifications of iRPCs

To operate under HL-LHC conditions while maintaining a hit efficiency above 95%, an improvedversion of the technical RPC design is introduced for the new iRPCs. From the layout point of view,the chambers are similar to the existing wedge-shaped RPC detectors with radially oriented readoutstrips placed between the gaps. An iRPC chamber consists of two gaps, i.e. top and bottom, eachmade of two High Pressure Laminate (HPL) electrodes coated with a thin graphite resistive layer.Unlike the present RPC design, the strips are integrated in a large trapezoidal printed circuit board(PCB) made of two parts. Each PCB comprises 96 readout strips in total, with a pitch of about 12.3mm in the high radius (HR) section and about 6 mm in the low radius (LR) section. Two Front EndBoards (FEBs) containing the front-end electronics are directly plugged into the PCB. Comparedto the existing RPC system, the new readout scheme offers a better spatial resolution and reducesthe number of electronic channels by 60% [4]. The new layout scheme also has the additionaladvantage of facilitating the cabling layout and the chamber construction because the strip signalshave to be extracted from only two sides of the chamber and not from different partitions as inthe present RPCs. To reduce possible aging effects and to improve the rate capability [5], thethickness of the electrodes as well as the gas gaps are reduced from 2 mm to 1.4 mm. A reductionin the efficiency is avoided by amplifying the signal and increasing the sensitivity of the front-endelectronics system five times compared to the existing system [6]. By improving the front-endelectronics and simultaneously reducing the gas gap thickness, the avalanche charge is effectivelyreduced, and hence the rate capability and chamber longevity are enhanced. Following this newlayout, the high-voltage working point of the iRPC detector is also reduced from 9.5 to 7.1 kV. Anexploded view of an iRPC chamber is shown in Fig. 4.

Figure 4: Schematic view of an iRPC detector.

– 4 –

5 New front-end electronics for iRPCs

With the new layout of the iRPCs, the amount of charge deposited by a charged particle passingthrough the detector is reduced compared to the present CMS RPCs. The front-end board (FEB)of the present system does however not support detecting the lower charges without affecting thedetector performance. Therefore, a new FEB equipped with low noise front-end electronics that candetect signals with a charge as low as 10 fC was designed and developed. It is fast and reliable andhas the ability to survive in the high radiation environment. The front-end electronics of the iRPCsis based on the Petiroc ASIC, which is a 32-channel ASIC using a broad band fast preamplifierand a fast discriminator in SiGe technology [7]. Its overall bandwidth is 1 GHz with a gain of 25,and each channel provides a charge measurement and a trigger output that can be used to measurethe signal arrival time. The new PCBs offer the possibility to readout each strip from both ends,yielding two signals per pitch. Profiting from the excellent time resolution (20–30 ps [8]) of theelectronics and by measuring the arrival time difference of the two strip ends of the 2D readoutscheme, it is able to determine the position along the strip with good resolution of about 200 ps or1·7 cm [9].

To validate the performance of iRPCs with the new front-end electronics, different studies withthe proposed FEB were conducted using a muon beam under different irradiation conditions at theCERN Gamma Irradiation Facility (GIF++) [10]. Although the GIF++ source produced a uniformirradiation all over the chamber during the test, the presence of a lead shield resulted in differentirradiation fluxes over different regions of the iRPC. This variation allowed the study of the impactof the electronics dead time on the iRPC efficiency under a high flux counting rate up to 2 kHz·cm.The top (bottom) plot in the Fig. 5 shows the efficiency measured at a low (high) irradiation withan average rate of ∼ 0.038 (1.790) kHz·cm−2 with respect to the effective high voltage (HV𝑒 𝑓 𝑓 ) onthe gaps and also the variation of the hit multiplicity (<M>) according to the HV𝑒 𝑓 𝑓 [11]. Evenat the high background rate, around a factor 3 higher than that expected in the HL-LHC period,efficiencies above 95% were obtained at the chamber working point. The light red (dark black) lineshows the efficiency with the signal detected on the HR (LR) side. The efficiencies were measuredat a position close to the HR side of the chamber. The slight difference in efficiencies observedbetween the HR and LR sides is due to the signal loss through propagation along the strip. ThePCBs equipped in the chamber used for this test were made of Flame Retardant (FR4) material witha dielectric constant of about 4.3. The loss of efficiency arising from the signal attenuation whenpropagating along the strips is expected to be reduced by developing the next version of the strippanels with EM888 material of dielectric value 3.7 [12].

6 iRPC demonstrators

To study the detector behaviour under real LHC conditions such as high background rate, noise,magnetic field, etc.; to validate the iRPC FEB and backend electronics; and to integrate the newRPC stations into the CMS detector control software and data acquisition system, a number of iRPCdemonstrator chambers will be installed in CMS during the ongoing, 2nd LHC Long Shutdown.This project will also lead to acquiring installation expertise in the CMS-RE3/1 and RE4/1 regions.The production center of HPL panels for iRPCs as well as RPCs is the Riva Laminati company

– 5 –

Figure 5: Efficiency versus effective HV at a low irradiation (top) and high irradiation (bottom).The hit multiplicity per event is also reported [12].

(Milan, Italy), and the gaps are produced at the Korean Detector Laboratory. Eight demonstratorchambers (5 RE3/1 and 3 RE4/1) were assembled in July 2021 at Ghent University (Belgium). Gap-level as well as chamber-level Quality Control tests (QCs) were performed on the site followingstandardized protocols. The gap level QC includes visual inspection of the gaps, verification ofthe spacer conditions and gas tightness, and dark current measurements. The gas tightness test andspacer test for iRPCs are conducted at an overpressure of 15 hPa above atmospheric pressure. Figure6 shows the plots of the gap-level QC tests performed for a demonstrator gap. In the gap-level QCtest, a positive pressure of about 15 hPa is applied to each gap and the pressure drop is measured asa function of time, as shown in the plot 6a. The leak rate, i.e. slope of the linear fit (light red line) ofthe data (dark blue), for the acceptable gap should be less than 0.04 hPa/min. The plot 6b shows themonitored pressure for the spacer test. The dark blue trend shows the data and the horizontal lightred line in the upper part of the plot shows the threshold for considering the spacer as a popped up

– 6 –

(a) Leak test (b) Spacer test

(c) Dark current test

Figure 6: The gap level QC plots of the CMS iRPC demonstrator chamber.

one. Each spike in the plot corresponds to a spacer in the gap. The transitions show that the spacersare in good condition. For the HV test, the dark current is monitored at 16 HV points. The plot6c shows the variation of the dark current with respect to the applied HV, which is in agreementwith the expected trend. As shown in the plot, at 5 kV the iRPC gap becomes fully ohmic and theworking point is at 7.1 kV.

After the assembly, a visual inspection of the chamber mechanics is performed and the gas leaktests and dark current tests are repeated to verify the status of the gaps. All chambers are shipped tothe RPC laboratory at CERN and the remaining QC, which include the long term chamber stabilitycheck and the cooling circuit, electronics, and cosmic muon tests are ongoing. Four qualifiedchambers out of the eight are scheduled for installation on the CMS endcaps in November 2021.

7 Summary

As part of the effort to maintain the robustness and redundancy as well as the identification andreconstruction capabilities of the CMS muon system during the HL-LHC period, several upgrades

– 7 –

are being implemented to the CMS RPC system. The present RPC Link System is being upgradedto make the RPC system robust against background noise and to fully exploit the intrinsic timeresolution on the order of 1.5 ns of the iRPC chambers. To extend the current RPC pseudorapiditycoverage up to |[ | = 2.4, 72 new iRPCs will be added to the 3rd and 4th endcap stations. An updatedtechnical layout is proposed for the iRPCs in which the thickness of the gas gaps and the RPCelectrodes are reduced from 2 to 1.4 mm, to offer a short recovery time for the avalanche chargethrough the RPC electrodes, enhancing the chamber rate capability and reducing possible effectsof detector aging. The RPC upgrade also includes the replacement of the present readout system.The performance of the new front-end electronics was validated at the Gamma Irradiation Facilityat CERN, i.e. an efficiency above 95% was measured at a high particle rate of 1.79 kHz·cm−2,which proves the capability required for reliable operation under HL-LHC conditions. As part ofthe iRPC demonstrator project, eight chambers built at Ghent University are undergoing detailedperformance studies at CERN. The installation of these iRPC demonstrator chambers in CMS isscheduled for November 2021.

Acknowledgments

The corresponding author would like to acknowledge the support of the FWO-Flanders (Belgium,project no. I002319N), and to express her sincere thanks to the iWoRiD-2021 conference committeefor organizing the workshop.

References

[1] R. Adolphi et al. The CMS experiment at the CERN LHC. JINST 803 (2008) S08004.

[2] CMS Collaboration. The phase-2 upgrade of the CMS muon detectors. CERN-LHCC-2017-012(2017) [CMS-TDR-016].

[3] B. Boghrati et al. CMS phase-II upgrade of the RPC Link System. JINST 16 (2021) C04001.

[4] S. Meola et al. Towards a two-dimensional readout of the improved CMS Resistive Plate Chamberwith a new front-end electronics. JINST 16 (2021) C04001.

[5] G. Aielli et al. Improving the RPC rate capability. JINST 11 (2016) P07014.

[6] K. S. Lee et al. Study of thin double-gap RPCs for the CMS muon system. J. Kor. Phys. Soc. 73 (2018)1080.

[7] J. Fleury et al. Petiroc, a new front-end ASIC for time of flight application. IEEE NSS/MIC (2013) 1.

[8] F. Lagarde et al. High rate, fast timing glass RPC for the high [ CMS muon detectors. JINST 11(2016) C09006.

[9] K. Shchablo et al. Performance of the CMS RPC upgrade using 2D fast timing readout system. Nucl.Instr. Meth. 958 (2020) 162139.

[10] R. Guida et al. GIF++: A new CERN Irradiation Facility to test large-area particle detectors for theHigh-Luminosity LHC program. PoS ICHEP2016 (2016) 260.

[11] P. Paolucci et al. CMS Resistive Plate Chamber overview, from the present system to the upgradephase I. JINST 8 (2013) P04005.

[12] K. Shchablo et al. Front-end electronics for CMS iRPC detectors. JINST 16 (2021) C05002.

– 8 –